The present invention relates to a device for purifying fluids and in particular to a reverse osmosis device for use, for example, in sterilizing and purifying fluids serially through at least two reverse osmosis stages, for use in a system for medical drug formulation and delivery and for other end use applications.
The purification or separation of fluids using synthetic membranes can be advantageously used in many industrial, medical and home applications. Typical membrane separation processes include gas and vapor diffusion, dialysis, ultrafiltration and reverse osmosis.
Synthetic polymeric membranes can be applied to gaseous systems to separate gaseous solutions into their components. The membrane used in the gaseous systems must be permeable and selective, possess chemical and physical stability and be free of structural irregularities such as pinholes. The containing vessel should be capable of supporting these membranes under large pressure differentials; have a large membrane surface area per unit volume; cause a minimum pressure drop in the gas streams; and be inexpensive, i.e., be constructed of low-cost materials which are easy to fabricate and assemble. An example of such gas separation using synthetic membranes is the recovery of helium from natural gas and of oxygen from air. Such membrane separation processes, however, are often not competitive to known cryogenic processes because of the high power requirements for membrane separation.
Synthetic polymeric membranes have been applied to dialysis wherein some solutes selectively permeate through the membrane based on the concentration gradient across the membrane. While the dialysis process is not particularly rapid, it has been industrially utilized, for example, in the recovery of caustic from rayon and the recovery of spent acid from metallurgical liquors.
Ultrafiltration typically involves the separation of large solute particles from the solvent of the solution by forcing the solvent to pass through a membrane while the particles are retained to a greater or lesser extent. Often the separation involves a physical sieving of the particles which are retained on top of the membrane filter. For membranes of low pore radius, however, the process of ultrafiltration begins to overlap the process of reverse osmosis wherein the physical sieving phenomena is increasingly replaced with the adsorption and solubility of the solute within the membrane. The retained solutes consequently can have significant osmotic pressures which must be overcome by higher fluid pressures.
Hemodialysis is an example of a dialysis process which is assisted by ultrafiltration. A hemodialyzer is a membrane-containing device which is able to remove certain waste products such as urea, creatinine and uric acid from the blood. The patient's blood is introduced into the hemodialyzer preferably under the patient's own perfusion pressure and flows past the membrane which is typically cellulose. The blood solutes containing the waste then permeate through the membrane and into the dialysate, a sterilized solution formulated to control solute permeability through the membrane. Because osmosis may result in the undesirable net transfer of water from the dialysate into the blood which may result in edema, hemodialysis is often utilized in conjunction with ultrafiltration to remove the excess water. The dialysate can be prepared by the combination of purified water, produced by reverse osmosis, and the desired concentrate.
Reverse osmosis using synthetic polymeric membranes has been used for a variety of industrial end products. Such processes include the desalination of sea water and the processing of food and beverages. The alternative method of processing is by distillation. However, because of the high energy requirements of distillation, reverse osmosis processes compare favorably as the most economic route. Furthermore, for solutions susceptible to degradation at high temperatures such as fruit juices, reverse osmosis may be the most practical manner of processing the solutions while preventing substantial loss of desirable components in the original solutions.
An important use of the reverse osmosis process in the medical field is its application to peritoneal dialysis therapy. A generalized discussion of peritoneal dialysis therapy is discussed and described in U.S. Pat. No. 4,239,041 to Popovich et al. In particular, the Popovich patent discusses a fluid infusion method for continuous, ambulatory peritoneal dialysis (CAPD). The CAPD process differs from the more popular hemodialysis process in that it utilizes the body's natural peritoneal membrane in order to provide for the function of the artificial kidney. The CAPD process, however, while being ambulatory, is performed during the patient's normal, daily routine and requires treatment several times during the day. For this reason, the patient must remain by the dialysate supply during the entire period of treatment. This obviously will conflict with the patient's daytime activities and/or job requirements.
Alternatively, peritoneal dialysis can be performed at a hospital or clinic which requires that the patient visit the facility in order to obtain the required treatment. Such a visit requirement also has its inherent limitations on the normal activities of the patient.
Peritoneal dialysis is also generally discussed and described in the "Handbook 6010, Automated Peritoneal Dialysis", 1979 which is incorporated herein by reference. This handbook was distributed by B-D Drake Willock, a division of Becton, Dickenson and Co. in New Jersey and discusses that dialysate which is prepared from purified water can be infused into the patient's peritoneum through a catheter. Dialysis of the patient's blood through the peritoneal membrane and into the purified water region then occurs, allowing the body to excrete water, metabolites and toxins, and to regulate fluid, electrolyte and acid-base balance. The waste dialysate is subsequently drained out of the body. Peritoneal dialysis can be performed by various methods such as continuous and intermittent, as explained in Miller et al. "Automated Peritoneal Dialysis Analysis of Several Methods of Peritoneal Dialysis", Vol. XII Trans. Amer. Soc. Artif. Int. Organs p. 98 (1966).
Problems related to peritoneal dialysis include the difficulty in maintaining sterile conditions so as to prevent infection and the complexity of operating currently available peritoneal dialysis systems. A peritoneal dialysis device manufactured by Physio-Control Corporation of Redmond, Wash. is generally described in "PDS 400 Service Manual P/N 10454-01 July, 1981" which is also incorporated herein by reference. The device purifies the source water using a reverse osmosis module which is formed of a plastic housing containing a spiral wound membrane of cellulose triacetate. The device mixes the purified water with concentrate to form a dialysate, and then delivers the dialysate to the patient. The system controls the dialysate delivery at a set inflow rate and period and a set outflow period. An alarm is sounded and the system is turned off if various parameters are not within the set ranges. The parameters include the dialysate temperature, the dialysate conductivity, the inflow and outflow volume, and the system overpressure. The Physio-Control device is made up of two subsystems; the RO unit and the proportioning and monitoring unit. The device is bulky and complex in operation and requires extensive training of either the medical personnel or the patient that operate it. Additionally, extensive preventive maintenance is required to keep the system operational. Such maintenance includes the replacement of the RO pre-filter, filters and O-rings within the device every 500 hours of use as well as the cleaning of the RO sump pump. In addition, the device requires cleansing with bleach every 100 hours. Moreover, an extensive disinfection with formaldehyde must be performed before patient use if the sterile path has been broken during the functional test, calibration or adjustment of the device.
Another peritoneal dialysis device was designed by Ramot Purotech Ltd. The device employs RO membrane filtration through an RO cell formed of a large number of small membranes supported on plastic plates. After mixing the filtered water with concentrate to form the dialysate, the dialysate is fed by gravity to the patient. The outflow from the patient is also done by gravity into a waste bag. The need to connect the dialysate to the patient, leads to difficulties in maintaining sterile conditions.
Yet another peritoneal dialysis system is disclosed in U.S. Pat. Nos. 4,586,920; 4,718,890; and 4,747,822 to Peabody. The patents recite a continuous flow peritoneal dialysis system and process in which a continuous flow of sterile dialysis fluid is produced and caused to flow through the peritoneal cavity of the patient is a single-pass open circuit. A gravity fed system is utilized to flow the fluid into the patient's peritoneum. The pressure of the peritoneum and the volume of fluid into the peritoneum are monitored to ensure efficient and comfortable peritoneal dialysis. The pressure monitors of the system are capable of controlling the flow of fluid into the peritoneum. This system, however similar to others previously discussed, does not address the manner in which sterile conditions may be maintained nor the daunting complexity of operation required to be performed by the patient or care giver to use and maintain the system.
These and other problems have been solved in part by another device for peritoneal dialysis treatment called the Inpersol Cycler.TM. 1000, the Handbook of which is incorporated herein by reference. The Cycler.TM. is used to perform peritoneal dialysis in continuous cycling peritoneal dialysis (CCPD) and intermittent peritoneal dialysis (IPD) applications. The Cycler.TM. 3000 is used to not only perform CCPD and IPD but also tidal peritoneal dialysis (TPD). The Cycler.TM. is portable and is designed to be used in the home as well as in the clinic or hospital. In typical CCPD applications the exchanges are made at night while the patient is sleeping. A portion of the final dose is retained in the peritoneum during the day and drained out at the beginning of the nightly exchanges. The cycler system includes the cycler control unit and the stand. The stand holds the cycler unit, and fresh and spent dialysis fluids. The cycler control unit contains the warmer, weighing system, valving system and control electronics.
Notwithstanding the Cycler.TM., the problems of other known peritoneal dialysis devices have been solved by the present invention which is directed to a reverse osmosis (RO) filtration device for purifying water and for use in a user friendly automatic home dialysis system which will permit the patient to obtain peritoneal dialysis during sleeping hours. In this fashion, the patient will be free to conduct his normal activities during his waking or business hours without the interference of dialysis treatment. Additionally, the RO device and system of the present invention provide a self-contained, compact and sophisticated system whereby peritoneal dialysis is automatically performed and continuously controlled so as to allow the patient to undergo peritoneal dialysis at home with minimal need for patient intervention. This permits the patient to lead a more natural and fuller life than permitted under known treatment procedures.
The RO device and system of the present invention also provide for a low cost, efficient means to produce solutions of sufficient sterility, low pyrogen content and low dissolved mineral content for many other industrial and medical applications. Because of the compactness of the apparatus and its ease of use, purified fluids such as sterile and pyrogen-free water can be produced on site as needed without the inconvenience and cost of storing large quantities of the purified fluid. When applied to purifying water, the invention produces water of sufficient sterility such that the purified water can be employed in peritoneal dialysis, irrigation of patients during surgery or postoperative therapy, and pharmaceutical production for oral and intravenous administration. Additionally, the RO device can produce sterile water for the formulation of dialysate solution required in hemodialysis treatment. The purified water as produced by the device and system of the present invention can satisfy U.S.P. requirements as presented in the United States Pharmacopeia, The National Formulary P1456-1574, 1596-1598, 1705-1710, Jan. 1, 1990, US PXXII United States Pharmacopeial Convention, Inc. Also, the RO device and system avoids any need for terminal sterilization as required by known peritoneal dialysis devices.
Alternatively, the RO device and system of the present invention may be adapted to supply sterile water for the formulation of dialysate for use in hemodialyzers. The hemodialyzers in turn use the dialysate to purify the patient's blood in a manner currently used in hospitals and clinics.
For less demanding processes where sterility is not a major concern, the RO device and/or system of the present invention may be adapted to dialysis and ultrafiltration processes. Typical end use applications include those previously discussed such as the recovery of spent caustic or acid solutions from industrial production liquors (i.e. rayon steep liquor and metallurgical liquor).
The present invention is also directed toward the method of manufacturing the RO device in a manner which would minimize the cost of manufacturing and expedite it as well. Assembly steps include the application of adhesive in an automated manner by roller coating, induction bonding, sonic welding, and radiation sterilization.